In conventional imaging using an X-ray computed tomography (CT) device, imaging for positioning is performed to collect a positioning image (a scanogram) before main imaging. In imaging using an X-ray CT device, for example, auto exposure control (AEC) is performed that calculates a tube current to be supplied to the X-ray tube in main imaging based on the collected positioning image.
When calculating a tube current using the AEC, a standard deviation (SD) is used as an index of image quality. In modern reconstruction methods, however, because the relation between the tube current and the SD is non-linear, graininess and the noise power spectra (NPS) may be different from what are expected. Expected image quality is therefore less likely to be obtained.